abstract: Semiconductor device scaling has kept up with Moore's law for the past decades and they have been scaling by a factor of half every one and half years. Every new generation of device technology opens up new opportunities and challenges and especially so for analog design. High speed and low gain is characteristic of these processes and hence a tradeoff that can enable to get back gain by trading speed is crucial. This thesis proposes a solution that increases the speed of sampling of a circuit by a factor of three while reducing the specifications on analog blocks and keeping the power nearly constant. The techniques are based on the switched capacitor technique called Correlated Level Shifting. A triple channel Cyclic ADC has been implemented, with each channel working at a sampling frequency of 3.33MS/s and a resolution of 14 bits. The specifications are compared with that based on a traditional architecture to show the superiority of the proposed technique. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

abstract: Carrier lifetime is one of the few parameters which can give information about the low defect densities in today's semiconductors. In principle there is no lower limit to the defect density determined by lifetime measurements. No other technique can easily detect defect densities as low as 10-9 - 10-10 cm-3 in a simple, contactless room temperature measurement. However in practice, recombination lifetime τr measurements such as photoconductance decay (PCD) and surface photovoltage (SPV) that are widely used for characterization of bulk wafers face serious limitations when applied to thin epitaxial layers, where the layer thickness is smaller than the minority carrier diffusion length Ln. Other methods such as microwave photoconductance decay (µ-PCD), photoluminescence (PL), and frequency-dependent SPV, where the generated excess carriers are confined to the epitaxial layer width by using short excitation wavelengths, require complicated configuration and extensive surface passivation processes that make them time-consuming and not suitable for process screening purposes. Generation lifetime τg, typically measured with pulsed MOS capacitors (MOS-C) as test structures, has been shown to be an eminently suitable technique for characterization of thin epitaxial layers. It is for these reasons that the IC community, largely concerned with unipolar MOS devices, uses lifetime measurements as a "process cleanliness monitor." However when dealing with ultraclean epitaxial wafers, the classic MOS-C technique measures an effective generation lifetime τg eff which is dominated by the surface generation and hence cannot be used for screening impurity densities. I have developed a modified pulsed MOS technique for measuring generation lifetime in ultraclean thin p/p+ epitaxial layers which can be used to detect metallic impurities with densities as low as 10-10 cm-3. The widely used classic version has been shown to be unable to effectively detect such low impurity densities due to the domination of surface generation; whereas, the modified version can be used suitably as a metallic impurity density monitoring tool for such cases. / Dissertation/Thesis / M.S. Materials Science and Engineering 2013

Supercapacitors have emerged in recent years as a promising energy storage technology. The main mechanism of energy storage is based on electrostatic separation of charges in a region at the electrode-electrolyte interface called double layer. Various electrode materials including carbon and conducting polymers have been used in supercapacitors. Also, supercapacitors offer high life cycle and high power density among electrochemical energy storage devices. Despite their interesting features, supercapacitors present some disadvantages that limit their competitivity with other storage devices in some applications. One of those drawbacks is high self-discharge or leakage. The leakage occurs when electrons cross the double layer to be involved in electrochemical reactions in the supercapacitor’s electrolyte. In this work, the first research project demonstrates that the addition of a very thin blocking layer to a supercapacitor electrode, can improve the energy storage capability of the device by reducing the leakage. However, the downside of adding a blocking layer is the reduction of the capacitance. A second project developed a mathematical model to study how the thickness of the blocking layer affects the capacitance and the energy density. The model combines electrochemical and quantum mechanical effects on the electrons transfer responsible of the leakage. Based on the model, a computational code is developed to simulate and study the self-discharge and the energy loss in hypothetical devices with different thicknesses of the blocking layer. The third research project identified the optimal amount of a surfactant (Triton-X 100) that had a significant effect on the double layer capacitance and conductivity of a spin-coated PEDOT:PSS (poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)) electrode. The effect of the concentration of the surfactant was investigated by measuring the electrochemical properties and the conductivity of different electrodes. The electrodes were fabricated with different concentrations of the surfactant. Scanning electron microscopy characterizations confirmed the structural change in the PEDOT:PSS that contributed to the capacitance and conductivity enhancement. A final research project proposed an approach on how to utilize the modified PEDOT:PSS added to different photoactive dyes to design a photoactive supercapacitor. The new approach showed the possibility of using a supercapacitor device as an energy harvesting as well as a storage device.

Orientador: José Alexandre Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T16:42:08Z (GMT). No. of bitstreams: 1 Lima_LucasPetersenBarbosa_M.pdf: 10518299 bytes, checksum: abe557fa5f682bd296c9fb416948d523 (MD5) Previous issue date: 2011 / Resumo: Filmes de nitreto de titânio (TiN) e nitreto de tântalo (TaN) foram depositados sobre substratos de Si (100) utilizando um sistema de sputtering reativo, com diferentes fluxos de N2 (10-80 sccm) e potência (500-1500W), em ambiente de N2/Ar. Foram analisadas as influências da mistura gasosa N2/Ar e potência nas propriedades estruturais e elétricas dos filmes de TiN e TaN, utilizando as técnicas de perfilometria, microscopia de força atômica, 4 pontas, espectroscopia Raman, difração de raios-x e espectroscopia de fotoelétron. As análises físicas e elétricas dos filmes de TiN e TaN demonstram que os filmes são policristalinos, com as orientações preferenciais (311)-( 111) e (200)-( 111), respectivamente. Os valores das taxas de deposições, resistividades elétricas e tamanho de grão para os filmes de TiN e TaN estão entre 4 e 78 nm/min, 150 e 7500 ??.cm e 0,001 e 0,027 ?m2, respectivamente. Foram fabricados capacitores MOS e diodos Schottky com eletrodos superiores de TiN e TaN com dielétricos de SiOxNy ou SiO2, e extraídas curvas CV e IV destes dispositivos, para extração de parâmetros como tensão de flatband (VFB), densidade de carga efetiva (Q0/q) e função trabalho do eletrodo superior (WF). As curvas CV dos capacitores MOS com dielétrico de SiOxNy e eletrodo superior de TiN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 cm2, 0,29 V e 4,65 eV, respectivamente, que são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiOxNy e eletrodo superior de TaN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 cm2, 1,36 V e 3,81 eV, respectivamente, que não são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiO2 e eletrodo superior de TiN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 e 1012 cm2, de 0,12 V e 0,36 V, e, 4,15 eV e 4,43 eV, respectivamente, que são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiO2 e eletrodo superior de TaN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 e 1012 cm2, 0,29 V e 0,20 V, e, 4,41 eV e 4,44 eV, respectivamente, que são compatíveis com a tecnologia CMOS. Estes resultados indicam que os filmes de TiN e TaN são compatíveis para serem utilizados em dispositivos da tecnologia MOS / Abstract: Tantalum nitride (TaN) and titanium nitride (TiN) films have been obtained by DC sputtering, using different nitrogen flow (10 - 80 sccm) and power (500 - 1500 W), in a nitrogen (N2)/argon (Ar) ambient on Si (100) substrates. The N2/Ar ratio in gas mixture and power effects on structural and electrical properties of TaN and TiN films were investigated by scan profiler (film thickness and deposition rate), atomic force microscopy (rms roughness and grain size), fourprobe technique (electrical resistivity), Raman spectroscopy, x-ray diffraction (crystal orientation) and X-ray photoelectron spectroscopy (film composition). The physical and structural analyses of TiN and TaN films show that TiN and TaN films were polycrystalline, with (311)-( 111) and (200)-( 111) preferred orientation, respectively. The deposition rates, electrical resistivities and grain size values of TiN and TaN films were between 4 and 78 nm/min, 150 and 7500 ??.cm and 0,001-0,027 ?m2, respectively. MOS capacitors and Schottky diodes were fabricated with TiN and TaN as upper electrodes and dielectrics with SiOxNy or SiO2. CV and IV measurements were carried out on these devices and flatband voltage (VFB), effective charge density (Q0/q) and metal gate work function (WF) were extracted from these measurements. The extracted values of Q0/q, VFB e WF 1010 cm2, 0,29 V e 4,65 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiOxNy as gate dielectric. The extracted values of Q0/q, VFB e WF 1010 cm2, 1,36 V e 3,81 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiOxNy as gate dielectric. The extracted values of Q0/q, VFB and WF were about 1010 and 1012 cm2, 0,12 V and 0,36V, and 4,15 eV and 4,43 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiO2 as gate dielectric. The extracted values of Q0/q, VFB and WF were about 1010 and 1012 cm2, 0,29 V and 0,20V, and 4,41 eV and 4,44 eV, and these values were extracted from CV curves of MOS capacitors with TaN as gate electrode and SiO2 as gate dielectric. These extracted values for VFB and WF indicates that the TiN and TaN films are suitable for MOS technology / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

L'autonomie énergétique est un verrou majeur au déploiement massif de réseau de capteurs sans fil dans nombreuses applications. La récupération d'énergie et son stockage constituent une voie pour améliorer cette autonomie. Dans certaines applications en environnement sévère ou nécessitant des durées de vie élevées, l'utilisation de batteries pour le stockage est prohibée. On a alors recours à du stockage sur supercondensateurs. Ce type de stockage présente des inconvénients nécessitant un compromis entre 3 facteurs : la charge rapide des supercondensateurs (capacité faible), l'énergie maximale stockée (capacité forte) et la maximisation de l'usage de l'énergie stockée (tension résiduelle basse). Pour répondre à ces critères apparemment contradictoires, nous avons proposé trois architectures de stockage auto-adaptatif. La première est composée d'une matrice de quatre supercondensateurs identiques, interconnectés par des interrupteurs, dont la capacité équivalente s'adapte à l'énergie stockée. Les deuxième et troisième architectures sont constituées de deux supercondensateurs, l'une de capacité faible et l'autre de capacité grande, la différence entre les deux architectures étant liée au nombre et type d'interrupteurs utilisés. Les architectures de stockage auto-adaptatif que nous avons proposées incluent une circuiterie de contrôle appropriée autoalimentée et permettant de faire varier la capacité apparente du dispositif. De plus, chaque architecture permet un démarrage à froid avec des supercondensateurs complètement vides. Ces trois architectures ont d'abord été optimisées en simulation puis validées expérimentalement en composants discrets. Finalement, nous avons implémenté l'architecture de stockage auto-adaptatif à deux supercondensateurs au sein d'un système de mesure sans fil complet utilisant une source de récupération d'énergie et son électronique associée pour son alimentation et montré la pertinence de cette approche de stockage reconfigurable. En termes d'efficacité d'usage de l'énergie, elles permettent d'atteindre jusqu'à 94,7% en composants discrets, valeur qui pourrait être encore améliorée en version intégrée sur silicium à la fois pour la circuiterie de contrôle et les supercondensateurs. / Energy autonomy is a major challenge in the massive deployment of wireless sensor networks in numerous applications. Energy harvesting and storage can serve as solutions to the autonomy issues. However, the harsh environment of certain applications requires a long lifetime since the use of batteries for storage is prohibited. We then resort to storage on ultra-capacitors. This type of storage has disadvantages that require a compromise between 3 factors: the fast charge of ultra-capacitors (low capacity), the maximum energy storage (strong capacity), and the maximization of stored energy utilization (low residual voltage). To meet these seemingly contradictory criteria, we propose three self-adaptive storage architectures. The first consists of a matrix of four identical ultra-capacitors, interconnected by switches, whose equivalent capacity adapts to the stored energy. The second and third architectures consist of two ultra-capacitors, one of low capacity and the other of large capacity, the difference between the two architectures being related to the number and type of switches used. The self-adaptive storage architectures that we propose include a suitable self-powered control circuitry to vary the apparent capacity of the device. In addition, each architecture allows a cold start with completely empty ultra-capacitors. These three architectures were first optimized through simulation, and then validated experimentally with discrete components. Finally, we implemented the self-adaptive storage architecture with two ultra-capacitors in a completely wireless measurement system, using an energy harvesting source and its associated electronics for its power supply, and demonstrated the relevance of this approach of reconfigurable storage. In conclusion, we deduce that the topologies can reach an efficiency of energy usage of up to 94.7% by employing discrete components, a value that could be further improved through the exploitation of a silicon integrated version for both the control circuitry and the ultra-capacitors.

No description available.

Fluctuation in the demand for electrical power and the intermittent nature of the supply of energy from renewable sources like solar and wind have made the need for energy storage a dire necessity. Current storage technologies like batteries and supercapacitors fall short either in terms of power output or in their ability to store sufficient energy. Pseudocapacitors combine features of both and offer an alternative to stabilize the power supply. They possess high rates of charge and discharge and are capable of storing much more energy in comparison to a supercapacitor. In the quest for solutions that are economical and feasible, we have investigated Prussian Blue in aqueous electrolytes for its use as a pseudocapacitor. Two different active materials based on Prussian Blue were prepared; one that has just Prussian Blue and the other that contains a mixture of Prussian Blue and carbon nanotubes (CNTs). Four electrolytes differing in the valence of the cation were employed for the study. Cyclic voltammetry and galvanostatic charge-discharge were used to characterize the electrodes. Our experiments have shown specific capacitances of Prussian Blue electrodes in the range of 140-720 F/g and that of Prussian Blue-CNT electrodes in the range of ~52 F/g. The remarkable capacity of charge storage in Prussian Blue electrodes is attributed to its electrochemical activity ensuring surface redox and its tunnel-like structure allowing ease of entry and exit for ions like Potassium. Simple methods of synthesis have yielded specific capacitances of the order of hundreds of Farads per gram showing that Prussian Blue has promise as an electrode material for applications needing high rates of charge-discharge.

No description available.

No description available.

No description available.